Selective oxidation of alcohols using octahedral molecular sieves: influence of synthesis method and property-activity relations

Manganese oxides having a tunnel structure (OMS-2) have been utilized as selective catalysts for alcohol oxidation. In this study manganese oxide catalysts were synthesized in different media and modified by exchanging the tunnel cation by H+, using acid treatment or exchanging with NH4+ followed by thermolysis. Various alcohol oxidations were performed using these catalysts to ascertain the influence of synthesis method on their activity. A correlation is made between lattice oxygen instability and activity of the catalysts, which indicates involvement of the lattice oxygen in the mechanism. The exchange of the tunnel cation with the smaller H+ ions leads to weakening of the Mn-O bond, as verified by temperature programmed desorption (TPD) results. Only the chemisorbed oxygen on the surface (O-) and the lattice oxygen in the layers close to the surface is involved in the oxygen transfer during the reaction. (C) 2003 Elsevier B.V. All rights reserved.